You mean the upper and lower front grills, the air intakes at rear, the side mirrors (assuming you have the plain black ones) right?  No rocket science here, this is an easy job.  I didn't even bother sanding before, just washed and scrubbed with detergent and water, then wiped thoroughly with rag saturated with rubbing alcohol.  Use Satin Black rattle can paint, not Glossy or Flat.  A couple light coats with adequate drying time in between.  Looks great, have had no issues with paint adhesion.  No, I didn't use paint meant for plastic, just standard all purpose paint from Ace Hardware or the like.
Also have painted wiper arms and door handles with similar great results; for these metal parts, I did use a red Scotch-brite pad prior to painting.

RichSan Diego

      From: Edward V Barger <edvbarger@MAC.COM>
 To: vanagon@GERRY.VANAGON.COM 
 Sent: Monday, January 16, 2017 12:58 PM
 Subject: Painting the black plastic trim on the out side
   
Need to get the tail lights front turn signals etc  painted this week so can put them back in and get the van tuned up and then smogged by the end of the month

Some time  fairly recently there was a discussion on such can that be found in some archives ? I have copied much from the day to day discussions and have it in my 
VW file but not this one 

Thinking I need to wet sand with 400 + grit then jus use black spray can paint  any thing else to watch for 

thanks for any and all help 

ed

Edward V Barger
edvbarger@mac.com
310 922 6251